342 - How often to trim up?

buggyjdav

This is my first bigger boat, had a 20 foot Sea Ray with an I/O, I worked the trim quite a bit on that boat when in shallow water. I am wondering how often you would trim up on a 342 in normal operation?

Black_Diamond

You'll want to start out fully trimmed down, once you start up on plane you'll just have to nudge the drives up until you start losing speed..as for shallow water, you need at least 36" not including waves for depth with the drives down.  I personally stay in 5-8' of water..but I can easily be in 2' waves at the beach.

LaRea

From the soon-to-be-released FAQ:

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How should I adjust my trim tabs and outdrive trim?

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For boats with outdrives, adjusting the outdrive trim (drive position) and trim tabs can give you a free improvement of 5-10% in speed or fuel economy, so it’s worth learning how to do it.  Trim tabs can also level your boat and give you more control in certain conditions. 

The exact settings are different for every boat because they depend on hull shape, power, load and other factors.  In general, for a given throttle setting, the boat is properly trimmed when you are going the maximum speed you can achieve without “porpoising” (bow bouncing up and down). Here’s how to find your boat’s sweet spot:

First, bring the boat to a comfortable cruise speed with the outdrives all the way down, and trim tabs fully retracted (“bow up”).  Note your speed and RPMs.  Next, start trimming the drives up a little bit at a time without changing the throttle setting.  You should find that as you raise the outdrives, your speed will go up slightly.  Continue slowly raising the drives until you hear the propellers start to ventilate (RPMs rise quickly, but the boat slows down).  Ventilation is the sign that your drives are too far up, and you should move them back down slightly.  Find the drive position that gives you the highest speed.  You will probably be going 2-3 mph faster than when you started.  

At that point, you might find that the boat is porpoising.  There are two ways to reduce porpoising: put the trim tabs down slightly, or move the outdrives down slightly, or both.  Experiment until you find the setting that eliminates porpoising without slowing the boat too much.  That is your boat’s sweet spot.  

With practice, you can easily trim the boat in 10-15 seconds every time you get on plane.  

Read this thread for information on adjusting trim tabs:

http://rinkerboats.vanillaforums.com/discussion/3356/trim-tabs-101 ;

See this thread for discussions about adjusting outdrive trim and trim tabs together:

http://rinkerboats.vanillaforums.com/discussion/2829/trim-tabs-or-trim-outdrives/p1 ;

JC290

LaRea you're doing a nice job with FAQ 

LaRea

Thanks!  We'll probably post it within a few days.

Stodge

Is Ventilation the same as Cavitation?

Dream_Inn

LaRea, let's just make sure that one is quoted since I picked it up from the Bennett tab guy.  Thanks for posting it though!

MarkB

Stodgy I believe he meant to say cavitation.

LaRea

Ventilation and cavitation are different beasts.  Ventilation happens when the prop pulls in air from the surface.  Cavitation happens when low pressure on the metal of the propeller surface causes water to "boil" into small bubbles of vapor.  

When you raise the drive too high, normally what happens is ventilation.

LaRea

DI -- which part needs to be quoted?

Stodge

Thanks for the info.

MarkB

LR with the low postive head on the propeller when it is trimmed up I wouldn't be surprised if there was cavitation occurring. 

LaRea

Maybe both.  I had always assumed that if the props are undamaged and correctly sized, it would be ventilation.  But honestly, I don't have any solid reason to assume it's not cavitation.  

Luckily, that distinction doesn't matter in the current context.  I'll edit the FAQ to say only that the propeller slips, and not speculate about the cause.